Question

x+y=216, 20x+10y=3780

Answer 1

x+y=216 ×(-10)

-10x-10y=-2160 (1)

20x+10y=3780 (2)

Adicionando (1) e (2) membro a membro temos:

-10x-10y+20x+10y=-2160+3780

10x=1620

x=1620/10

x=216

x+y=216

216+y=216

y=216-216

y=0